1. Field of the Invention
The present invention is directed to sealing Organic Light Emitting Diodes (OLEDs) and displays made of OLEDs.
2. Technical Background
As a result of the many potential applications for compact and efficient displays, organic light-emitting diodes (OLEDs) are the focus of a tremendous amount of attention. OLEDs include electrodes and organic layers. There are two types of electrodes an anode and a cathode. There are also two types of organic layers a conducting layer and an emissive layer. In conventional implementations, the OLED components are deployed on a first substrate. The first substrate is typically made of clear plastic, glass, or foil. A second substrate that is made of similar material is used to cover the OLED. The first substrate and the second substrate are hermetically sealed with a frit, encasing the OLED in a package (i.e., glass package).
During operations, the anode and the cathode (i.e., two electrodes) facilitate the flow of current through the glass package. When electricity is applied to the OLED, charge carriers (holes and electrons) are injected through the electrodes into the organic layers. As holes and electrons flow and are combined between the organic layers photons are produced to generate light.
In a number of applications OLEDs are considered as the replacement technology for the next generation of Liquid Crystal Display (LCD) and Light Emitting Diode (LED) based applications. Conventional OLEDs have a number of advantages. For example, OLEDs are found to be thinner, lighter, and more flexible than the crystalline layers in an LED or LCD. Since the light-emitting layers of an OLED are lighter, the substrate of an OLED can be flexible instead of rigid. In addition, OLEDs are brighter than LEDs, do not require backlighting like LCDs, and consume much less power than LCDs. These advantages are especially important for battery-operated devices such as cell phones and mobile computers. Lastly, OLEDs are easier to produce, can be made to large sizes, and have large fields of view. As a result of these advantages, current applications for OLEDs include small-screen devices such as cell phones, personal data assistants (PDAs), digital cameras, as well as large-screen applications such as the big-screen televisions of the future.
However, OLEDs do have a number of shortcomings. Conventional OLED manufacturing is very expensive. One issue is that OLEDs are susceptible to damage from exposure to the atmosphere. Exposing the organic layers to moisture and oxygen may cause a reduction in the useful life of an OLED. For example, OLED performance rapidly degrades in the presence of even a minute amount of moisture. To address this problem, during manufacturing, an OLED must be hermetically sealed.
In conventional OLEDs, hermetic sealing is accomplished by dispensing a frit pattern between two substrates and melting and sealing the frit to create a hermetically sealed air-tight glass package. Conventional methods of melting and sealing the frit pattern are performed with a laser.
There are a number of problems with forming a hermetic seal by using convention laser sealing methods. Electrical leads exit the glass packet to connect the OLED to other circuits. As a result, the sealing process must accommodate the electrical leads when creating the hermetic seal. Therefore, the frit must be deployed and the laser must be applied in such a way that a hermetic seal is maintained in spite of the electrical leads that cross the frit pattern.
In addition, using a laser causes a variety of negative thermal effects on the OLED. For example, the frit pattern must be dispensed on the substrate far enough away from the organic material so that the laser sealing process does not cause a thermal defect in the organic material. In addition, non-uniform laser characteristics may cause thermal damage. For example, if the laser changes in intensity profile, power, or beam size, etc., the laser may cause a non-uniform bond across the width, and length of the frit pattern, resulting in a poor hermetic seal.
One conventional method of laser sealing uses an optical mask to mitigate the problems associated with sealing across electrical leads and the thermal effects that result from sealing. However, the mask reduces useful laser power for sealing and as a result, impacts the quality of the seal and time required for sealing. Ultimately, quality and time impact the cost to manufacture and the useful life of an OLED-based product.
Therefore, it would be beneficial to address the problems associated with laser sealing an OLED. It would be beneficial to laser seal without the mask which impacts speed and quality. Lastly, it would be beneficial to seal in a manner that improves sealing strength and seal uniformity, which would ultimately increase the lifetime of OLED-based products.